Communications: directive radio wave systems and devices (e.g. – Determining velocity – Combined with determining distance
Patent
1998-06-05
2000-06-06
Sotomayor, John B.
Communications: directive radio wave systems and devices (e.g.,
Determining velocity
Combined with determining distance
342110, 342115, 342 70, G01S 1360
Patent
active
060724242
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for measuring the speed of a vehicle relative to the ground by means of radar, using the reflection of electromagnetic waves from the roadway.
2. Description of the Related Art
The speed of a vehicle relative to the ground is conventionally measured by using the rotary speed of the vehicle wheels, and more particularly of the nondriven wheels. However, in certain cases, such as if these wheels lock during braking or in vehicles with all-wheel drive, this speed measurement may be erroneous. Hence other methods for measuring the speed have been proposed, for example utilizing the Doppler effect.
From the prior art, for instance U.S. Pat. No. 5,243,564, a device for measuring the speed of a motor vehicle is known that utilizes the modification, caused by the Doppler effect, of the frequency of an ultrasonic wave transmitted by the vehicle and reflected by the ground back to it. In this reference, it is proposed that one of the problems associated with this type of measurement, in this case the influence of the horizontal position of the vehicle on the measurement be compensated for by means of a device using the rotary speed of the wheels, measured by an antilock brake system, to determine a load transfer angle of the vehicle. However, aside from the fact that such a system is expensive because it requires equipping the vehicle with an antilock brake system, the measurement that can be obtained with it can still be incorrect. In fact, especially if an electromagnetic wave (radar wave) is employed to improve precision, difficulties are still encountered from numerous perturbation factors intrinsic to the traffic field. In particular, the wave reflected to the receiver in the vehicle may have traversed multiple courses or have been reflected by parasitic targets. As a consequence, the frequency analysis performed to extract the speed information may easily be perturbed by these conditions and lead to erroneous results, which are all the harder to detect since they are at least plausible.
SUMMARY OF THE INVENTION
Hence the object of the present invention is to furnish a method for measuring the speed of a vehicle relative to the ground, the results of which have increased reliability without requiring additional equipment.
These objects of the invention as well as others which will become apparent from the ensuing description, are attained by a method for measuring the speed of a vehicle relative to the ground, of the type using the deviation in frequency associated with the Doppler effect between a transmitted wave sent by radar solidly connected to the vehicle and a reflected wave reflected by the ground, characterized in that radar of the type allowing simultaneous measurement of the relative distance and the relative speed between the radar and a target is used, and that the distance measurement is used to validate the speed measurement.
In an important characteristic of the present invention, the speed measurement is eliminated, if the associated distance measurement is not within a predetermined range of distance that brackets a fixed distance corresponding to the distance of the radar from the ground. Advantageously, this distance range may be variable as a function of the measurements of the vehicle speed made previously.
Further characteristics and advantages of the method of the invention will become apparent from the ensuing description and from a study of the appended drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a vehicle equipped with a device for measuring the speed in a situation that involves risks of perturbation;
FIG. 2 is a diagram of the waves transmitted and received by radar of the FMCW type, which is useful for the sake of comprehension of the invention; and
FIG. 3 is a flowchart of the method of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Turning to FIG. 1, a motor vehicle 1 equipped with radar 2 is shown. This radar transmits an electromagnetic wave 3
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Cremona Patrick
Kunert Martin
Greenberg Laurence A.
Lerner Herbert L.
Siemens Automotive S.A.
Sotomayor John B.
Stemer Werner H.
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